Add an option to make bucket notifications synchronous (#17406)

With the current asynchronous behaviour in sending notification events
to the targets, we can't provide guaranteed delivery as the systems
might go for restarts.

For such event-driven use-cases, we can provide an option to enable
synchronous events where the APIs wait until the event is successfully
sent or persisted.

This commit adds 'MINIO_API_SYNC_EVENTS' env which when set to 'on'
will enable sending/persisting events to targets synchronously.

cmd/handler-api.go

@@ -52,6 +52,7 @@ type apiConfig struct {
 	disableODirect              bool
 	gzipObjects                 bool
 	rootAccess                  bool
+	syncEvents                  bool
 }
 
 const cgroupLimitFile = "/sys/fs/cgroup/memory/memory.limit_in_bytes"
@@ -166,6 +167,7 @@ func (t *apiConfig) init(cfg api.Config, setDriveCounts []int) {
 	t.disableODirect = cfg.DisableODirect
 	t.gzipObjects = cfg.GzipObjects
 	t.rootAccess = cfg.RootAccess
+	t.syncEvents = cfg.SyncEvents
 }
 
 func (t *apiConfig) isDisableODirect() bool {
@@ -353,3 +355,10 @@ func (t *apiConfig) getTransitionWorkers() int {
 
 	return t.transitionWorkers
 }
+
+func (t *apiConfig) isSyncEventsEnabled() bool {
+	t.mu.RLock()
+	defer t.mu.RUnlock()
+
+	return t.syncEvents
+}